While there are many edible plants that can be foraged from the wild (mushrooms, asparagus and onions among many others), broccoli isn't one of them.
Broccoli is a human invention. It was bred out of the wild cabbage plant, Brassica oleracea . It was cultivated to have a specific taste and flavor that was more palatable to people.
Here's how that worked. Wild cabbage has small flower buds and is a biennial. That means it only flowers every other year.
In a controlled environment, it can be forced to reproduce itself many times. When an offspring of the plant with larger, tastier buds grows, gardeners threw away the less tasty plants and started reproducing from that one.
In future generations, there were further opportunities to get plants with larger, tastier buds. And other genes that make the process easier, such as plants that have a faster growing cycle emerged.
In selecting and reinforcing the traits enjoyed by more people, humans took wild cabbage and cultivated a new kind of plant altogether, broccoli.
Brassica oleracea isn't just the source of broccoli. Its cultivars (a word for plants that can only be produced via selective breeding) include cauliflower, kohlrabi, kale, brussels sprouts, and the cabbages found in grocery stores.
Burgess, Chuck, and Joey Williamson. "Wild Garlic & Wild Onion." Clemson Cooperative Extension. September 2016. Accessed November 15, 2016.
Druyan, Ann and Sagan, Carl. Shadows of Forgotten Ancestors. New York: Random House, 1992.
Tredwell, Emma. "Brassica Oleracea (wild Cabbage)." Kew Gardens. Accessed November 14, 2016.